TACTICAL AIR NAVIGATION (TACAN) - GlobalSecurity.org

More documents

Recommendations

Info

Figure 2-2.—Distance measuring round-trip travel time. second, per airborne equipment, to supply the necessary distance data. However, the total pulse out put of the transmitter constantly varies, according to the number of interrogating aircraft. In addition, random noise may trigger the transmitter. transmitter, as shown in figure 2-4. If few interrogations are being received, the gain and squitter of the receiver increase and add noise-generated pulses to the pulse train. If more interrogating aircraft come into range, the gain and squitter decrease and reduce the number of noise-generated pulses. The relationship between the gain and the number of pulses is such that only a 2-dBm change in sensitivity occurs between reception from 1 aircraft and those from 100 aircraft. An added advantage of using a constant duty cycle is that overall transmitter power drain remains constant. BEACON-TRANSPONDER IDENTIFICATION CODE Figure 2-3.—TACAN pulse train. For the transponder to provide azimuth information, the average power supplied to the antenna must be relatively uniform over time. To accomplish this, the transponder is operated on the constant-duty-cycle principle. In this method of operation, the receiver uses automatic gain and squitter (noise generated output) controls to maintain a constant pulse output to the Before an aircrew can use TACAN information that its equipment receives, it must positively identify the transmitting TACAN station. To meet this need, the ground station transmits an identification code at approximately one-half minute intervals. It does this by momentarily interrupting the transponder distance data and squitter-generated output with pulse groups spaced at a 1350-pps rate. Each pulse group contains two sets of 12-µsec pulse pairs spaced 100 µsec apart. The duration of the identification pulse groups varies, to represent Morse-coded characters. The duration for a dot is 100 to 125 ms, and for a dash 300 to 375 ms. An identification group is shown in figure 2-4. 2-2
Figure 2-4.—Transponder output pulse train. 15-HZ-BEARING INFORMATION The rf energy from the TACAN transmitter is fed to the antenna central element, which has no The timing of the transmitted pulses supplies the directivity in the horizontal plane. Parasitic elements actual distance information to the aircraft. This leaves positioned around the central element are amplitude modulation as another medium for the electronically rotated (switched on and off) at 15 transponder to convey other information to the revolutions per minute. (See the section below on the aircraft. The TACAN beacon-transponder modulates OE-273(V)/URN antenna group). The distance the strength of the pulse to convey bearing information between the central element and the parasitic elements by producing a specific directional-radiating pattern is selected to obtain a cardioid radiation pattern. To rotated around a vertical axis. This signal, when an aircraft at a specific location, the distance data properly referenced, indicates the aircraft’s direction pulses appear to contain a 15-Hz amplitude-modulated from the TACAN facility. This signal and distance signal because of the rotation of the cardioid radiation data give a two-piece fix (distance and direction) for pattern. This pattern is shown in figure 2-5, view A determining specific aircraft location. and view B. 2-3
Page 1: CHAPTER 2 TACTICAL AIR NAVIGATION (
Page 5 and 6: Figure 2-6.—TACAN modulation enve
Page 7 and 8: It may be mounted in its own cabine
Page 9: TACAN SET AN/URN-20 Though not mode

TACTICAL AIR NAVIGATION (TACAN) - GlobalSecurity.org

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?